The article “SENSE: Sensitivity Encoding for Fast MRI”, by Klaas P. Pruessmann et al., Magnetic Resonance in Medicine 42:952-962 (1999) describes a concept for considerably enhancing the performance of magnetic resonance imaging by means of arrays of multiple receiver coils. It discloses sensitivity encoding (SENSE) which is based on the fact that receiver sensitivity generally has an encoding effect complementary to Fourier preparation by linear field gradients. The use of an array of simultaneous receiver coils enables the scan time to be reduced and the resolution to be increased. The described method takes advantage of undersampling or reduction of k-space samples and also of known individual coil sensitivity profiles. Since sampling is performed with a step size larger than prescribed by the Nyquist theorem, the so-called foldover occurs during the (always necessary) Fourier transformation, so that in principle two different points from the physical image space cannot be distinguished from one another.
In practice the anatomical region to be examined asks for more coil elements and receiver channels that are provided as hardware in the MRI apparatus. An MRI apparatus produced and sold by Philips, that is, the Gyroscan NT which is also used in practice, can handle up to six synergy/phased array coils simultaneously by using six receiver channels, but certain applications could require more receiver channels and RF coils. If there are more RF coils than receiver channels, it is necessary to select coils for allocation to the available receiver channels. A larger number of receiver channels is possible in principle and would lead to shorter acquisition times or higher resolutions. But each additional receiver channel increases the costs of an MRI apparatus considerably, and each change in the number of receiver channels necessitates a redesign of the entire system, because more bandwidth is then required.